Nowadays in modern skiing success of a skier specializing in cross-country skiing, biathlon, alpine skiing, ski jumping and Nordic combination depends not only on his physical fitness, morale and skill, but also on the proper choice of skis or the type of ski sliding surface made of different materials with or without grooves of different materials with or without grooves of different shape and width, as well as the type of wax applied to the ski sliding surface.
In view of varying snow properties (e.g., due temperature and humidity changes) determining the ski sliding surface friction against the snow, proper selection of the sliding surface type and wax necessitates accurate and timely (on the day of competition) measurements of sliding properties (dynamic friction) and track-holding properties (static friction) of different types of ski sliding surface and ski waxes.
The majority of skiers choose skis and ski wax experimentally by means of multiple testing of a limited number of various ski sliding surfaces and waxes. It is a time-and effort-consuming procedure which, nevertheless, does not yield sufficiently accurate results. That is why when choosing skis, type of their sliding surface and wax sportsmen and coaches rely mostly on personal experience and intuition.
Prior art devices for testing the ski sliding surface smeared with wax or without it due to their structural features do not provide for accurate and timely selection of a desirable type of skis, ski sliding surfaces and waxes.
There is a prior art device for ski wax selection (URSS Inventor's Certificate No. 188340. Int.Cl. A63C 11/04, published in the official bulletin "Otkrytiya, Izobreteniya, Promyshlennye Obraztsy, Tovarnye Znaki", 1966, v. 21) comprising a mock-up ski with ski wax applied to its sliding surface and a percussion mechanism for propelling the mock-up ski on the snow designed as a spring-loaded pusher. The device is intended to determine the sliding properties of different waxes on the basis of measuring the mock-up ski sliding distance when it comes forward.
This device is rather slow in operation as it takes quite a long time to propel the mock-up ski, measure the sliding distance and return the mock-up ski to the initial position. Such a device shows low accuracy of sliding properties measurement due to substantial influence of static friction (with speed approaching zero) and roughness of the snow on which measurements are conducted and also limited functional abilities as the ski wax choice is based only on sliding properties measurement.
A prior art device for testing the ski sliding surface (cf. USSR Inventor's Certificate No. 787051, Int.Cl. A63C 11/04, published in the official bulletin "Otkrytiya, Isobreteniya, Promyshlennye Obraztsy, Tovarnye Znaki", 1980, v. 46) comprises a case housing accommodating a spiral spring one end of which is attached to the case and the other--to an axle, a support bushing an exterior end of which holds a disk whose end face intended for interaction with snow or imitation surface is made of a material forming the test ski sliding surface, and a mechanism for measuring relative rotation of the disk and the case.
The mechanism for measuring relative rotation of the disk and the case contains a limb with a scale and a knob, and also an overrunning clutch for recording the relative rotation value defining snow or imitation surface holding capacity of the test ski sliding surface with ski wax applied to it.
After the device has been set up on the snow the knob of the limb is turned. The spiral spring connected with the limb and the support bushing starts winding up thus giving rise to a growing torque on the support bushing. Winding continues until the torque exceeds the moment of resistance created by the snow-holding force of the test ski sliding surface. The disk together with the support bushing rotates in the same direction with the limb, the starting moment of the rotation being determined by observation, and the knob turning is stopped, while the twist angle value is registered on the scale. The starting moment of the disk rotation is determined owing to the clearance between the limb and the case being jammed by a ball of the overrunning clutch when the relative rotation direction is reversed. On the basis of track-holding capacity measurements taken in the course of testing different disks having their end face smeared with various waxes one chooses the ski wax which is the most suitable under the given conditions.
Said prior art device for testing the ski sliding surface has but limited functional abilities as the described design of the gadget for measuring relative rotation of the disk and the case makes it possible to measure only the track-holding capacity value.
Accuracy of measurements is not high due to the overrunning clutch having a significant dead zone and thus determining the starting moment of the disk rotation with inadequate precision. Rotation of the case by means of the knob attached to it adversely affects the pressure of the device on the snow and causes its displacement that makes the starting moment of the disk rotation too early or too late. The device design does not rule out the possibility of inadvertent measurement errors.
The prior art device is also rather slow-acting and inconvenient in operation, since to take each measurement it is necessary to zeroize the limb scale and to lift the device off the snow for reading out the results as the limb scale is on the case side panel.
Due to the fact that the support bushing of the prior art device has a large diameter and the disk is fixed by means of spring locks, considerable skewing of the disk axis and catching of the spring locks may occur thus increasing disk replacement time.